1. Field of the Invention
The present invention relates to electrical and electronic circuits and systems. More specifically, the present invention relates to systems and methods for protecting electrical and electronic circuits and systems from electro-static discharge.
2. Description of the Related Art
Many electronic circuits and systems are susceptible to being damaged by electrostatic discharges. An electro-static discharge is a charge transfer from a charged body, often a human, to ground or a terminal of opposite polarity. Electro-static discharges can generate energy with tens of thousands of volts. When voltages at this level are applied to unprotected and relatively delicate integrated circuits, damage often results. Not only can the operation of the device be momentarily impaired (with the consequent impairment of the operation of the host system and the data output thereby), but, it may also lead to permanent damage. In some cases, the damage to the circuits may be difficult to detect. In any event, it is therefore common in the art to provide some means and methodology for protecting components, circuits, and systems from electrostatic discharge.
One currently used technique for providing protection against electro-static discharge (ESD) is based on the use of a protection circuit consisting of two diodes connected between the device input, supply and ground to shunt positive and negative discharge voltages to supply and/or ground. Unfortunately, the conventional diode based ESD circuit has been found to be less than fully effective in that during an ESD event, until the diodes turn on, some current flows through the protected device or circuit instead of being shunted away by the diodes. If the device is not properly sized with respect to current handling ability, it may be permanently damaged by the event as discussed above.
Another approach has involved the use of a resistor in front of the device being protected. However, for circuits operating at radio frequencies (RF), resistors used for ESD protection adversely impact performance.
Hence, a need remains in the art for an improved electro-static discharge protection system or method, particularly for use with RF device, circuits and systems.
The need in the art is addressed by the system and method of the present invention. The inventive system includes an arrangement for protecting an element from electrostatic discharge and includes a mechanism for sensing a pulse of energy associated with an electro-static discharge and providing a control signal in response thereto. A switch is provided which inhibits the flow of energy through the element in response to the control signal.
In the illustrative embodiment, the switch is an n-channel field effect (NFET) transistor switch. The switch may be disposed between the element and ground, between the element and source of supply current, and in the input line of the element. In the first case, a resistor is disposed between the positive supply of the element and an input terminal of the transistor to provide a control voltage effective to keep the transistor on during normal operation. A capacitor is disposed between the input terminal of the transistor and ground. The RC time constant is chosen to be much larger than the time constant of the ESD pulse. Consequently, input voltage of the transistor will remain unchanged and the transistor will remain off preventing the element from conducting the pulse discharge current and providing ESD protection.